Progressive disseminated histoplasmosis is a common and life-threatening fungal infection among patients with HIV/AIDS in the United States and Latin America. Incidence rates in HIV/AIDS can be >20%, with mortality rates >30% in resource-limited countries where the fungus, Histoplasma capsulatum, is endemic. Early diagnosis and treatment are essential to reducing this high mortality rate. Diagnosis currently depends on culture or histopathology. These methods have low sensitivity, are time consuming, are expensive, and require trained personnel. An alternative approach is an immunoassay to detect H. capsulatum polysaccharide in serum or urine. The target antigen is believed to be a cell wall galactomannan. Studies to date have found a high sensitivity for such assays. However, immunoassay for Histoplasma antigen i) is currently available only in ELISA format through use of a reference laboratory, ii) is not commercially available for distribution in resource-limited countries, iii) is dependent on the use of polyclonal rabbit antibodies (pAbs), and iv) is not amenable to point-of-care (POC) use. Our overall hypothesis is that an immunoassay for POC diagnosis of disseminated histoplasmosis in HIV/AIDS can be constructed with high-affinity monoclonal antibodies (mAbs) that target the polysaccharide antigen of H. capsulatum that is shed into serum and urine during infection. A corollary to this hypothesis is that the use of appropriate pairs of mAbs for assay construction will enable targeting of common and unique H. capsulatum epitopes, providing a control over assay specificity that is not possible with pAbs. The first Specific Aim is to produce polysaccharide antigens suitable for screening of hybridomas and evaluation of mAb specificity. The second Specific Aim is to produce a library of mAbs reactive with the spectrum of epitopes found on the Histoplasma polysaccharide antigen that is shed into serum and urine. If the goals of this Phase I are achieved, Phase II will use mAbs from Phase I to construct and evaluate an immunoassay in POC format. Our preferred assay platform would be the lateral flow immunochromatographic (dipstick) assay. If successful, this translational research project could dramatically decrease mortality from histoplasmosis through earlier diagnosis and treatment. Importantly, this can be done at the low cost needed in resource-limited countries.